The overall goal of the proposed study is to determine the effectiveness of a multi-setting early intervention protocol in preventing problematic sequelae typically associated with Attention-Deficit/Hyperactivity Disorder-Combined Type (ADHD) in young children. Behavioral and academic interventions with established efficacy will be implemented in community settings (i.e., outpatient pediatric clinic, preschools, and homes) such that preschool-aged children with ADHD will be less likely to develop problems with aggression, academic underachievement and poor peer relationships. Further, it will be determined whether multi-setting early intervention can reduce utilization of medical services and whether continued treatment results in maintenance of effects. A sample of 200 3 to 5 year old children with ADHD will be randomly assigned to a Multi-Setting Early Intervention or a Community Intervention group. The Multi-Setting Early Intervention group will receive a treatment package (parent training, assessment-based behavioral intervention, and academic intervention) for one year and then will receive either a high-intensity or a low-intensity maintenance intervention over an additional 18 months. The Community Intervention group will receive intervention available in the community (e.g., psychotropic medication and special education services) and monthly parent groups delivering information about child development and medical functioning (i.e., attention control procedures). Dependent measures will include behavior ratings completed by parents and teachers, direct observations of behavior, academic performance indices, and archival data (e.g., medical and school records). Between group differences will be assessed on six occasions across four years. Results will be analyzed using both multivariate analyses of variance with repeated measures and hierarchical linear modeling.